Reduced Carbon Uptake by European Forests during the Summer Drought of 2022
A. van der Woude1,2
1University of Groningen, Centre for Isotope Research, Groningen, Netherlands; +316 48911050, E-mail: auke.vanderwoude@wur.nl
2Wageningen University, Department of Meteorology and Air Quality, Wageningen, The Netherlands
Recent years have seen repeated record breaking temperatures and high impact events such as floods, storms, and droughts across Europe, in line with the expected consequences of its +1.5 oC of warming over the past thirty years. In many metrics the 2018 summer drought has ranked top of the list for severity and impacts, including in reductions of carbon exchange by forests. Drought conditions thought unprecedented over the past 500 years trigger strong responses in forest, suffering from leaf-level vapor-pressure deficits and root-level moisture deficits simultaneously. We report here that in the summer of 2022 close to 30% of the European continent was again under severe or exceptional drought, with temperatures exceeding those even of 2018 and a similarly large size of area affected (3.4 million km2). Although a stationary blocking atmospheric pressure pattern over the Atlantic was responsible for both droughts, the 2018 event mostly affected northwestern Europe while the 2022 drought was centered over France. The more southerly centering exposed more drought resilient semi-arid vegetation which dampened the peak loss of carbon uptake by forests relative to 2018. Observations and models suggest that vapor pressure deficits rather than lack of soil moisture played a dominant role in reducing photosynthesis in 2022. Nevertheless we find a similar cumulative reduction of net ecosystem carbon exchange (~50 TgC less uptake) in 2022, with specifically high impacts in southern France where widespread summertime carbon release by forests, as well as extensive wildfires (emitting close to 5 TgC) occurred. Our analysis demonstrates a much improved capacity in our community to rapidly quantify drought impacts from the atmospheric and ecosystem monitoring network. However, strong impacts on eastern European broadleaf forests suggested from observed near-infrared reflection by vegetation and simulated by terrestrial carbon cycle models can not be confirmed currently through in situ observations, signaling an important gap in our capacity to track carbon exchange in the European terrestrial biosphere.